In the detection of optical image patterns of relatively low illumination intensity levels of the order of, or below, 10.sup.-.sup.11 watts per square centimeter, it is desirable to use a channel electron multiplier device for the purpose of converting the optical image pattern into a corresponding electron beam pattern. Such a device produces typically thousands of individual channel multiplier electron beams whose intensities are in accordance with corresponding portions of the optical image. In conjunction with such a channel electron multiplier, it would be desirable to have a compact sized detector for storing the electron channel beam cross-section pattern in a form which can be randomly accessed for readout at any desired portion, or combination of portions, of the cross section at any selected moment of time while the other portions of the device continue to store the electrons of the remaining electron beams, and hence continue to store the electrons of the remaining corresponding portions of the optical image pattern cross section for subsequent similar random access readouts.